LONDON, United Kingdom — Boris Johnson is under pressure to ask the European Union to postpone Brexit after Parliament refused to approve the deal the prime minister negotiated.

At a rare Saturday sitting, members of parliament voted to delay a decision on the agreement Johnson reached in Brussels this week until he has got the legislation that enacts it through parliament.

That leaves Johnson obliged by law to send a letter to Brussels requesting that Britain’s departure be delayed until January 31.

Speaking after the vote, Johnson said that he will not negotiate a delay with the EU.

But he still has a chance to deliver his pledge to get Britain out of the EU by the end of the month. A Withdrawal Agreement Bill will be put before parliament next week, and it could begin its journey into law as soon as Tuesday.

The question then will be, as it was on Saturday morning, whether Johnson has the votes to push it through. The day saw Conservative MPs, both current and almost all those he expelled last month, saying they’d vote with him, as well as a small number of Labour MPs. If he can hold that coalition together for two weeks, he might have a chance.

If he fails, the country will be plunged into an unprecedented political crisis. The possible outcomes range from delaying Brexit -- allowing time for a general election or a second referendum on leaving — to a chaotic and economically damaging departure from the bloc without a deal in just 12 days’ time.

If Johnson tries to circumvent the legislation forcing him to seek a delay, as his aides have previously threatened, he is almost certain to face legal challenges that could end up in the UK Supreme Court.

That makes it likely he will ask for an extension, something that would require the unanimous agreement of EU leaders.

On Friday, French President Emmanuel Macron said one shouldn’t be granted. But EU officials say that despite Macron, who made similar noises before approving a Brexit delay in April, it’s unlikely that he or any other leader would refuse another one, particularly if the UK was headed for a general election.

If attempts to stop a no-deal Brexit fail, the consequences for Britain are likely to be severe. According to the government’s own analysis, a chaotic no-deal Brexit would cause disruption to trade, financial services, and food supplies, and risk civil disorder.

By Robert Hutton and Kitty Donaldson; editors: Tim Ross, Edward Evans, James Amott.